(1) Field of the Invention
The present invention relates to a magnetic brush development process for forming a high-quality image by using a so-called two-component type developer in the electrophotography.
(2) Description of the Prior Art
In the electrostatic photography, there has been widely adopted a magnetic brush development process comprising supplying a two-component type developer comprising an electroscopic toner and a magnetic carrier onto a magnet sleeve to form a magnetic brush, and bringing the magnetic brush into sliding contact with the surface of a photosensitive material drum on which an electrostatic latent image is formed, to visualize the latent image and form a toner image.
In this magnetic brush development process, however, not only characteristics of the developer and photosensitive material but also various mechanical conditions such as the peripheral speed of the photosensitive drum, the peripheral speed of the magnet sleeve, the drum-sleeve distance, the magnetic intensity of the magnet sleeve and the cutting length of the magnetic brush are important as factors for obtaining a good image, and setting of conditions for obtaining an optimum image is very difficult and complicated.
By the optimum image is meant an image having a good image density and a good resolution. However, in general, the conditions for obtaining an image having a high image density are not in agreement with the conditions for obtaining an image having a high resolution, and it is very difficult to set the development conditions.
Recently, high-speed reproduction is eagerly desired, and if the rotation speed of the photosensitive material drum is much increased over the speed adopted in the conventional electrostatic photographic apparatus, other development conditions should be drastically changed and the above-mentioned disadvantage becomes more serious.
Furthermore, even if development conditions capable of providing a good image are set at the initial stage, when the developer or sleeve is deteriorated by the continuous reproduction for obtaining many prints, the agitating property and flowability of the developer, especially the brush-forming property, are changed and it becomes difficult to form an optimum magnetic brush, with the result that reduction of the image quality often takes place. This is especially conspicuous under high-temperature high-humidity undesirable conditions.